Insulated metal substrate (IMS) printed wiring board (PWB) construction includes either a single layer or two or more layer laminate having a surface mount printed circuit arrangement for receiving and mounting electrical components such as, for example, semiconductor devices thereon. The arrangement utilizes a plurality of electrically insulative and thermally conductive layers disposed on a highly thermal conductive layer which serves as the base layer for the assembly. The other layer forming the opposed surface normally serves as a circuitry array and/or surface mounting pad or arrangement for one or more solid state devices.
The two or more layer construction allows higher circuit trace density and the ability to route traces otherwise not possible in a single layer configuration. However, a two layer construction has a thermal resistance of about 2.5 to 3 times the thermal resistance of a single layer construction. Therefore, high power dissipating components are not as efficiently coupled to the metal base plate. Only about one-half of the power can be packaged into a two layer construction as compared to a single layer IMS. Therefore, the use of a two or more layer IMS construction has been employed in very limited applications.
A need has thus arisen for an improved IMS PWB with a two or more layer laminate and the capability of mounting high power dissipating components to the internal layer to yield improved thermal coupling to the metal substrate while improving the routing density over single layer IMS PWBs. Additional needs have developed for manufacturing methods of solder paste dispensing in the assembly process using such IMS PWBs.